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COLUMN: Lookout for invasive tree diseases

Rosanne LoParco
Sentinel columnist
Posted 8/21/22

Our precious trees are under attack by invasive insects and diseases. Some have spread rapidly and are causing economic and ecological impacts on our forests and urban trees.

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COLUMN: Lookout for invasive tree diseases


Our precious trees are under attack by invasive insects and diseases. Some have spread rapidly and are causing economic and ecological impacts on our forests and urban trees.

The New York State Department of Environmental Conservation’s (NYSDEC) Forest Health program is responsible for monitoring the ecological health and function of the forests of New York State. The program gathers, analyzes, and reports on tree pest and disease information.

We’ve heard about the insects. The Hemlock Woolly Adelgid (HWA) is an insect threatening hemlock trees. The Emerald Ash Borer (EAB) is an Asian beetle infesting North American ash tree species. The Asian Longhorned Beetle (ALB) is a wood-boring insect; its larvae bore into many species of hardwood trees. The newly discovered Spotted Lanternfly (SLF), first discovered in Pennsylvania in 2014, has spread to New York. It feeds on many different plants, including several shade trees.

Invasives are not just insects. There are also invasive diseases threatening New York’s biodiversity. Dutch Elm Disease, Chestnut Blight, Beech Bark Disease, and Thousand Cankers Disease attacking walnut trees are all disease threats. Also, be aware of:

Oak Wilt: This disease affecting oak trees is caused by a fungus. All oaks are susceptible; but red oaks are especially impacted. Its origin is unknown; it was first detected in Wisconsin in 1944. It has spread throughout the Midwest and Texas and has killed thousands of trees. In New York, Oak Wilt was first detected in Glenville; but despite a quick response to control it, additional infection sites have been found. It’s been verified in Suffolk, Kings and Ontario counties.

The disease is spread above ground by beetles and below ground through tree roots. Brown coloration develops on leaves with branch dieback at the top of the tree’s canopy. Leaves suddenly wilt in spring and summer and fall from the tree, typically while still green. Find more information about this disease by visiting the NYSDEC website’s fact sheet at

Beech Leaf Disease (BLD): This disease affects and kills both native and ornamental beech trees. It is associated with a nematode. This is a newly discovered problem and not much is known about it, including the full cause and how it spreads. BLD leaf defoliation is widespread through Westchester and Suffolk counties. Most recently, BLD has been discovered in 12 new counties including Sullivan, Chenango, Oswego, Steuben, Chemung, Schuyler, Yates, Wayne, Kings, Monroe, Tioga and Herkimer counties.

Symptoms of this problem are seen in the leaves; look for striping, curling, and/or a leathery texture to the leaf. Symptoms are visible from May until leaves fall off in October. Because so much about this disease is unknown, finding new infestations is critical. Find more information on the NYSDEC website,

For all of these invasive problems, it’s critical not to move firewood; follow New York’s firewood regulations and obey Quarantine Districts. Become familiar with all the insects and diseases attacking our precious trees. Visit the NYSDEC website or the St. Lawrence Eastern Lake Ontario Partnership for Regional Invasive Species Management (SLELO PRISM) website at

Help the DEC track BLD, Oak Wilt or other tree problems by using New York iMapInvasives. You can download the free iMapInvasives app on your GPS-enabled smartphone or device. If you don’t have access to a device, then send photos or information to the DEC at or call 1-866-640-0652.

Cornell Cooperative Extension Oneida County answers home and garden questions which can be emailed to or call 315-736-3394, press 1 and then Ext 333. Leave your question, name and phone number. Questions are answered weekdays, 8am to 4 pm. Also, visit our website at or phone 315-736-3394, press 1 and then Ext 100.


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